🛡️ Digital Signature Standard (DSS) in Java

Java implementation of the Digital Signature Standard (DSS) for message integrity and authenticity verification.

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Author: Shaina

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🎯 Aim

To implement the Digital Signature Standard (DSS) to generate and verify digital signatures, ensuring the authenticity and integrity of communicated messages.

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⚙️ How It Works

The Digital Signature Standard is implemented in the following phases:

1. Hashing the Message:

   • A custom hash function simulates a SHA-like hashing mechanism to generate a digest from the input message.

2. Key Generation:

   • Generate a private key x.
   • Calculate the public key y = g^x mod p, where g is the generator.

3. Signature Generation:

   • Use the private key to compute the signature components r and s using a fixed ephemeral key k.
   • These values are derived through modular exponentiation and inversion operations.

4. Signature Verification:

   • Using the public key, message hash, and the signature, the verifier computes a value v.
   • The signature is valid if v == r.

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🔑 Key Components

• modularExponentiation: Computes (base^exponent) mod modulus.
• extendedEuclidean: Finds GCD and the Bézout coefficients for modular inverse.
• findModularInverse: Used for computing modular multiplicative inverses.
• customHash: A deterministic hash function simulating SHA behavior.
• generateDSSKeys: Generates the private and public keys.
• createDigitalSignature: Computes the digital signature for a message.
• verifyDigitalSignature: Validates the authenticity of the digital signature.

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🚀 Steps to Run

1. Clone the repo

   git clone https://github.com/shaina-gh/DSS.git
   cd DSS

2. Compile and Run the Java File

   javac DSS.java
   java DSS

3. Expected Output

   Signature creation and verification results for both an original and a tampered message.

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🧪 Sample Output

Created Private Key: 3
Created Public Key: 18
Message Digest: 138972264302481705700123578240310737814155524
Ephemeral Value k: 1
Signature Component r
Signature Component s: 5
Verification Value v: 4
Signature Verification Result: True
Verification Value v: 1
Tampered Message Verification Result: False

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📚 Observation

Signature verification succeeds for valid, untampered messages.

Signature verification fails for tampered messages, proving the integrity of DSS.

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✅ Result

The DSS algorithm for digital signature generation and verification was successfully implemented in Java.

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